Decreased incidence of ventricular fibrillation after an acute coronary artery ligation in exercised pigs

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Abstract
Evidence has been presented that regular physical activity may be associated with a decreased incidence of sudden cardiac death. It has been suggested that selfselection of those engaging in regular exercise rather than the physical activity itself is a major factor in explaining these results. We therefore studied the effects of a two-month exercise program on the incidence of ventricular fibrillation after an acute ligation of the left anterior descending (LAD) coronary artery in domestic Yorkshire pigs. At the end of the exercise program, the exercised group (EG, n=17) had a lower heart rate (10%), a 5 times higher maximum exercise capacity, a 10% larger left ventricular mass and a thicker myocardial wall during end-diastole than a sedentary group (SG, n=13). After the animals were anesthetized, the LAD artery was occluded at one third of its distal end. Ventricular fibrillation (VF) occurred in 92% of the SG (12 out of 13) against only 30% of the EG (5 out of 17) within 1 hour after occlusion. Percentage of the area at risk was the same (9–10% of total left ventricular mass) in both the EG and SG. Transmural myocardial perfusion after coronary artery ligation was slightly larger in EG than in SG (30 vs 21 ml·min−1·100g−1, p<0.05). Although the improvement in perfusion of the ischemic zone of the EG may have contributed to the reduced occurrence of ventricular fibrillation, other mechanisms cannot be excluded.